The present invention relates to a diaphragm controller for a camera of the program type, and more particularly, to such a diaphragm controller for a camera of the program type which controls a diaphragm aperture so as to be determined by a predetermined program characteristic in response to the brightness of an object being photographed.
In a single-lens reflex camera of the program type which hitherto controls a diaphragm aperture based on a predetermined program characteristic, an open F value of a taking lens should be first introduced as an exposure information. Then the brightness value of an object being photographed is calculated based on the open F value introduced and a TTL (through the lens) photometric value at the open aperture of the taking lens. Thereby, a diaphragm aperture and an exposure period are determined from the calculated brightness value based on the predetermined program characteristic. Specifically, in a diaphragm control, a TTL photometry is conducted once at open aperture and the TTL photometric value is stored. Then, the diaphragm aperture is reduced and a TTL photometric value of light passing through a reduced aperture during the aperture reducing operation is compared with a predetermined value which is calculated based on the stored photometric value at open aperture. When both values coincide, a magnet for suspending the aperture reducing operation or the like is driven to suspend it. Accordingly, a conventional camera of the program type is generally provided with a transmitting member for transmitting an open F value of a taking lens to the camera. With a camera not provided with such a member, it is possible to conduct a diaphragm control based on a predetermined program characteristic.